Process of refining by selective solvent action



Fb.17,1942. 5 v 2,273,660

PROCESS OF REFINING BY SELECTIVHSOLVEKP ACTION Original Filed Feb. 14,1934 2 Sheets-Sheet 2 v RaFFmaTe Dissolved SohgenT So\ven1" ATTys.

Patented Feb. 17, 1942 PROCESS or REFININ BY SELECTIVE SOLVENT ac'rronJohn Ward Poole, Jaitrey, N. H.

Original application February 14, 1934, Serial. No.

Divided and this application January 12, 1938, Serial No. 185,387

13 Claims.

This invention relates to improvements in processes of refining byselective solvent action an incompletely refined substance, which may bea raw material, in a system in which counter-cur- 7 rent fiow of solventand the substance to be refined is utilized, which comprises maintainingsuch conditions in the terminal zones from which the spent solvent andthe rafilnate are respectively expelled as will result in the return tothe system of material whose properties are intermediate those of therafiinate and those of the extract and which would otherwise be includedin the extract or the raflinate, whereby an improved result in thequality of the ramnate, the quality of the extract, the yield of theraffinate, and/or the yield of the extract will be attained.

The present applicationis a continuation of my application Serial No.711,180 filed February 14,

1934, for Processes of refining by selective solvent action, which inturn is a continuation-m part of my copending applications: Serial No.

- 606,763, fi1ed April 21, 1932 (patented July 3, 1934,

No. 1,965,392), for Fractionating mixtures of hydrocarbons and theirderivatives; Serial No.

' hydrocarbon substance in a system in which a countercurrent'fiow ofthe solvent' and the substance to be refined is utilized which comprisescausing artificial precipitation, in the terminal zone from which thesolvent containing the extract is expelled, of a hydrocarbon substancedissolvedinfthe solvent entering the terminal zone, thereby tojproduce areflux of the precipitated substance whose properties are intermediatethosebf the extract and those of the rafllnate and which would otherwisebe included in the extract, thereby causing the extracting capacity ofthe entire system, or such selected portion thereof as will hereinafterappear, to be available for refining the precipitated materiaL- Suchprecipitation may be produced in various ways,

included in the raifinate and maintaining such conditions in all otherparts of the system as will cause the solvent to possess comparativelyhigh solvent power.

By suitably regulating the intensity of the precipitating means andconsequent artificial precipitation products of predetermined qualityand/or yield can be produced from the extract and/or the rafilnate.

The processfcrming the subject matter of the present invention isapplicable to the refinement the various constituents may be obtained.

The present invention while applicable to solvent extraction of manymixtures of soluble materials will be more specifically described withrespect to the treatment of mixtures of hydrocarbons and/or theirderivatives, all of which forsimplification will be referred to hereinas hydrocarbons, such as petroleum and materials derived therefrom forthe production of superior lubricating oils, and also for the productionof more desirable asphalts.

I have discovered that certain new and useful methods of operation ofsolvent extraction processes bear analogies to certain principles ofdistillation in important commercial technology based upon theseprinciples, reference to which will be made more clearly to explain thepresent invention.

as for example, by abruptly reducing the tem-' perature of the solventphase as it enters the For purposes of illustration and to avoid theintricacies of complete explanation of the principles of solventextraction, highly expert chemists in this art have frequentlychosen tospeak of phenomena of solvent extraction in greatly simplified terms. Inorder to explain the most important efiect of solvent extraction, thatof stances are homogeneous.

phasafthereby artificially producing a reflux materialwhich containssubstances desirably to be (2) That such two materials become mutuallyinsoluble each in the other when in the presence of a selective solvent.I

(3) That the solvent is insoluble in the undissolved material.

(4) That a component of the undissolved or rafllnate portion is entirelyinsoluble in the solvent, or if soluble dissolves in the same manner andin the same degree as it would if pure.

In actual practice it is usually found that these assumptions areinaccurate and that due consideration must be given .to the deviationfrom these assumptions in that complete recovery of either type ofmaterial is impossible since an unrecovered portion of each will beincluded in the other and the purity and quality of each therebyadversely afiected.

It is believed that the degree of inaccuracy of these assumptions hasnot heretofore been recognized. Since this invention relates to methodsof minimizing the'deviations and operations in accordance with thelimitations thereby imposed, a short discussion of these limitations isdesirable to the complete understanding of the invention.

For the purposes of illustration I will consider a material which is adistillation cut of petroleum derived by such careful rectification thatit may be considered as of essentially constant boiling point. In thispetroleum out there will exist hundreds, and perhaps thousands, ofdifferent compounds, each one of which under normal conditions ofoperation will be somewhat soluble in thesolvent used, and likewise eachwill probably be soluble to a different extent from each of. the others.Furthermore, they may not be divided into the two classes ofcomparatively insoluble and comparatively soluble material, but willvary from very slightly soluble compounds to those which by themselveswould be completely miscible with a solvent. However, it is true thatsaturated and highly paraffinic" material will be the least soluble andthat an unsaturated and aromatic material and hydrocarbon derivativeswill be highly soluble. Since all components are probably more or lesssoluble each in the other this mutual solubility will change the actualsolubility under the conditions of operation so that after an extractionor a series of extractions has been effected, and the original materialhas been divided into two fractions, a raffinate and an extract, sometrace of every component originally present will be found in bothfractions. Consequently, if extraction of sufli cient intensity is usedto produce a highly paraffinic" ramnate, there will result as acontaminant of the extract a very considerable loss of "paraffinicmatter. Conversely, if by mild extraction a highly naphthenlc" extractis produced, very considerable amounts of such material may be lost as acontaminant of the raflinate.

It is very probable that during extraction all components distributethemselves between the two phases, solvent and undissolved, according toa definite distribution ratio different for each compound. This beingtrue, it is also true, that as the concentration of any componentincreases, its concentration in each phase will increase in directratio.

If, therefore, a system can be so controlled that a gradient ofparafilnicity can be established varying from a high paramnicity to ahigher naphthenicity, and spent solvent issues from the system at theterminal of high naphthenicity, then the resulting extract will behighly and correspondingly naphthenic, and the more the concentration ofnaphthenic materials in the solvent terminal zone is increased the morenaphthenic the same component in the other phase, also present in acorresponding and definite concentration. Such is also true indistillation processes with regard to the dense and dispersed phases.

As a matter of fact, it is demonstrable that in both instances theequilibrium concentrations are those at which the partial vaporpressures in the respective phases are equal.

In distillation processes the carrying agent may be considered steam; insolvent extraction proc: esses the carrying agent is the solvent. Indistillation processes the stripping force is the partial vapor pressureof each component as it exists in the mixture'and under the conditionsmaintained. In the process by solvent extraction the force is thesolubility of the component in question as it exists under thecircumstances maintained. The degree of solubility of the component inquestion may be affected both by the solubility of the pure substance inthe solvent and also by its distribution ratio between the solvent andthat portion of the original material remaining undissolved.

In distillation the stripping force may be decreased by lowering thetemperature and vice versa. In solvent extraction a number ofalternative methods may be employed. For example, an increase intemperature will increase .the driving force since the solubility of allmateor incompletely refined substance, and the solwill be the extract,and conversely as the parafvent or solvents, are passed continuously ina countercurrent flow through a succession of stages each consisting'ofa mixingtdivision and a separating division. In such processes the oilor incompletely refined substance will enter and the solvent containingthe dissolved matter will leave at one terminal zone which may bedefined as the solvent terminal zone, while fresh solvent will enter andthe refined oil or raflinate containing a small quantity of dissolvedsolvent will leave at the other terminal zone which may be defined asthe raillnate terminal zone.

This process may also be employed in a tower in which the lighter of thetwo materialsthe solvent or the incompletely refined substanceisintroduced at or near the bottom and the heavier material introducedator near the top of the .tower. The lighter component therefore travelsupwardly through the column while the heavier component travelsdownwardly. Some mixing device is usually employedin the tower toimprove contact between the two phases and in consequence increase theeffectiveness of the solvent. Whether a tower or a system of succesthesame.

In'usual solvent extraction systems the whole system is maintained atsome temperature which is considered appropriate, or only one of thematerials entering the system is maintainedat an appropriatetemperature, it being considered that fluctuations in the temperature ofthe other component are so small as to be deemed unimportant, so thatthe operation is essentially at a fixed and predetermined temperature.

Such method is quite analogous to the stripping I operation carried outby counter-current fiow of fresh steam is always in contact ,with themate- I rial leaving the system and flows upwardly through the materialwhichpasses downwardly through the vessel, the vessel being of sumcientheight to give adequate contact Such a process would be much moreeconomical of steam (as isothermal counter-current solvent extractionwould be economical of solvent) than would be the case if the materialcontaining volatile matter were stripped with steam in a vessel where nocounter-current flow occurred,

and the material allowed -to mix without restraint. To complete theanalogy, in this latter case a more orless uniform temperature of suchmagnitude as to produce vapor pressures of the volatile material of suchmagnitude as to permit of satisfactory stripping action by the steamwoulctbe maintained. Such an operation would beclassiflable as'si'mplecontinuous distillation.

recovery of both the heavier and the lighter portions'in thatcontamlnations oi both products by the other will be reduced.

For the purpose of this analogy, between solvent extraction anddistillation, it is not necessary to discuss the part played by theportions In my invention I have resorted to methods which in contrast tosimple continuous distillation are analogous to continuousrectification. Rectification iseffected by maintaining in a rectifyingcolumn'a temperature gradient. This a temperature gradient is maintainedthrough input of heat at the bottom of a tower and removal of heat atthe top .of the tower. For most efiicient operation for given apparatusit is necessary that the heat be removed onlyfrom the I tower top as theremoval of the heat at intermediate points tends to reduce theefiiciency of the apparatus. I

, The effect of heat input atthe bottom is largely to vaporize materialwhich will contain a higher percentage of material of higher boilingpoint than is desirable for inclusion in the distillate. However, thisvaporized portion is richer in such distillate material than is thematerial from whichit is distilled and which is dischargedfrom thebottom of the tower as one of the final products. The effect ofthe-temperature gradient is to establish a corresponding concentration.gradient throughout the column. This heat .in-

put will result in a greater concentration of volatile material in theupper portion of the tower.

The removal of heat at the top of the tower results largely in thecondensation of material comprising both high boiling point material.

of the tower intermediate of the top and bottom, or the methods by whichinput and removal of heat may be effected. It will sufllce to say thateach plate ,or section of the tower, to a certain degree, repeats boththe effect of input and removal, neither will it be necessary to discussthe conditions in which the principle is applied in packed and platetowers.

One effect of plates is, however, pertinent to the analogy. In certaincases with the trinary or other multicomponent mixtures, it is possibleto have material of such intermediate volatility characteristics as tobe undesirable as a component of either the top or the bottom stream.Such material often develops a zone of maximum concentration at someintermediate point in the column. In the case of towers equipped withtrays this material may be continuously discharged as a side stream, itsquality and quantity being fixed by the specification requirements ofthe two primary products. By inserting catch basins of proper design itis also possible to withdraw side streams from a packed tower.

Another principle of rectification is, however, important in the analogybetweensolvent. ex-

traction and distillation which has an important bearing upon thepresent invention: To secure a combination of maximum purity andrecovery of both types of material, it is often necessary to supply thefeed at an intermediate point in the tower. Technically, the portion ofthe tower below the feed'is called the stripping section and thatportion above the point of feed the "rectifying section? Inpractice thepoint of feed is determined by the needs'of'the particular problem. Itis usually desirable to introduce the feed at that point where theliquid material in the column is most similar to the feed, althoughthere are cases in which either one section or the other may be omitted.

g In carrying out analogies between rectification processes and methodsof using solvent extraction, I have developed a complete mathematicaland graphical statement corresponding to that on 7 since the inclusionofall such necessary material would needlessly enlarge this specification.

' A specific example. of the application of this invention, usingcrotonaldehyde with approximately two per cent of moisture as a solventand a Mid-Continent overhead cylinder stock of approximately 200 secondsviscosity Saybolt Universal at 210 F. is as follows: First, using athree-stage countercurrent plant consisting of mixers and centrifugalseparators both the solvent and the oil terminal stages were maintainedat approximately degrees F. The result was to produce a rafiinate of25.8 A. P. I. in contrast to a charging stock of approximately 20 A. P.I. The extract removed had a specific gravity of approximately 1.02 andwas an asphalt of approximately penetration. Subsequently with no changein conditions of operation other than to increase the temperature of therafllnate terminal zone to around 100 F. results were as followst Theramnate possessed an A. P. I. gravity of 26.3, whereas the specificgravity of -the extract was decreased to approximately 1.01.

In neither case did the extract contain appreciable quantities ofparafllnic material since the lightest and in consequence mostparaillnic distillate produced from the second extract possessed aviscosity index of around minus forty indicating extremely lowparafllnicity. The net result of the operation was therefore to producea rafiinate of increased paraflinicity as shown. by

comparison of the A. P. I. gravities. The extract, on the other hand,although not as completely asphaltic as in the first instance, wasmaintained at an extremely high naphthenicity. It was found if bothterminal zones of the system were maintained at 100 degrees F. (thetemperature of the rafiinate teminal zone) that the process becamenearly inoperable, whereas the rafllnate re- 4 seconds Saybolt Universalviscosity at 100 F. was

charged to this same plant, crotonaldehyde of approximatelythree percent moisture being used as a solvent, temperature was maintainedessentially constant throughout the system at around 85 degreesFahrenheit, and it was found with simple operation of this system thatabout aavaoeo solvent to one part of oil. In actual practice thereshould be no limit to the actual rate of feed of the two primarymaterials as long as the fifty per cent of rafilnate of between 30 and31 A. P. I. gravity could be produced with about fifty per cent ofextract. No actual determination was made of the specific gravity ofthis extract, but upon injecting water as a precipitant to essentiallysaturate the solvent phase with water at 85 degrees F. there was aresultant precipitate of about thirty per cent of theoriginal charge,possessing a higher A. P. I. than did the original feed material,indicating in consequence a greater degree of parafllnicity.

This separated material was then returned to the system. It was foundthat the quantity of rafiinate based on the total through-put oforiginal stock was increased to approximately seventy per cent, with anessentially unchanged 'raffinate in that only .1 A. P. I. was lost.

It is, therefore, obvious that by meansOf the process above described agreat improvement in yield ofraflinate is secured and that the qualityof the extract is also improved.

Operation with other solvents, such as acrolein, nitro-benzene,furfural, or phenol, is similar to the cases outlined above, except thatin the case where that water is not miscible with the solvent employed amiscible precipitant such as acetone, acetaldehyde, or the like, wouldbe necessary.

In the cases already cited the rate of feed to the system wasessentially constant at about two gallons per hour. Flow of solvent inthe case of Mid-Continent cylinder stock was in the ratio of two volumesof solvent to one volume of oil. In the case of the Mid-Continentneutral flow was inpthe ratio of one and one-half parts of 76 properratio of feed is maintained.

Any limiting factors on the magnitude of operation in a single set ofunits would be one of engineering rather than theoretical consideration.For instance, if centrifuges were used as separators there is both anupper limit-and a lower limit of efficient design. If the bowl oi thecentrifuge is too small it becomes difllcult of adjustment. If toolarge, difllculties in manu= facture and balancing 'may result.

In the drawings:

Fig. 1 is adiagrammatic illustration of a suitable apparatus in whichcountercurrent flow is produced having means for performing the processabove described in its simplest form;

Fig. 2 is a similar diagrammatic view of a more complete apparatusprovided with means enabling it to perform the process in a manner moreeconomical with respect to the quality and/or yield of theresultingproducts;

Fig. 3 illustrates apparatus of the tower type having means enabling itto perform the process herein described.

In the drawings, Fig. 1 comprises two unit stages, the first having amixer l and a separator 2 of any desirable construction, such as acentrifugal separator or a U-separator, while the second stage comprisesa mixer 3 and a separator 4 which also may be a centrifugal separator ora U-separator. The raw or incompletely refined material is drawn from asuitable source (not shown) through a pipe 5 by a pump 6 and forcedthrough a pipe I into the mixer l. The pressure thus maintained in themixer forces the material through a pipe 8 into the separator 2. Thesolvent is similarly drawn from a suitable source (not shown) through apipe 9 by a pump l0 which forces it through a pipe ll into the mixer 3and the pressure thus maintained in the mixer 3 forces the material fromthe mixer through a pipe I! into the separator 4. Suitable conduits leadfrom the respective separators of one unit to the mixer of the otherunit in such a manner that a countercurrent flow through the system ismaintained and the spent solvent and extract carried thereby aredischarged from the separator 2 while the raffinate and a relativelysmall amount of dissolved solvent are discharged from the separator 4.

The operation of the process after the system has been filled with thesolvent and material to be refined and balanced is as follows: Thematerial to be refined, after having been forced from the mixer i intothe separator 2, is resolved into a solvent phase and an oil phase. Thesolvent phase containing the extract is discharged through the pipel3,while the oil phase is discharged through the pipe l4 into the mixer 3where it is mixed with the incoming fresh solvent and is discharged fromthe mixer 3 into the separator 4 where it is resolved into an oil phaseand a solvent phase and the oil phase or raflinate expelled through thepipe II. The solvent phaseproduced in the separator 4 is dischargedthrough the pipe l6 into the mixer I from which it is forced into theseparator 2 in the manner'above described.

In the present invention means are provided for maintaining suchconditions in those terminal zones in which the spent solvent andrafllnate are respectively expelled as will result in the return to thesystem from the solvent terminal zone of material whose properties areintermediate those of the railinate and those by providingheat-exchanging means of any suitable type for controlling thetemperature of the fiuid which is supplied to the respective separators.In Fig. l a coiled pipe l1, through which water may be circulated, isshown as surrounding the pipe 8, while a similar coiled pipe I8 is shownas surrounding the pipe II through which the solvent is supplied to themixer 3.

Suitable means, such as valves, are provided for controlling thecirculation of water, steam,

or other suitable heat-transporting fluid, through the respective pipes.

By suitably controlling the transfer of heat to the material passingthrough the pipes 8 and II a temperature gradient may be maintained inthe system which will cause the return to thesystem of materialwhose'properties are intermediate those of the raillnate and those ofthe extract. Some of such material will be directly precipitated andreturned from the solvent zone, while other portions of suchintermediate material will be returned by solution in the solvent in therafilnate zone and carried therefrom to the solvent zone. In this mannera gradient of parafilnicity is established through- 'out the systemwhich will resultin increased ,parafiinicity in the raifiriate andconversely decreased paraflinicity of-the extract in the spent solvent.

By abruptly reducing the temperature of the solvent phase as it entersthe terminal zone from which the solvent is expelled, a portion of thehydrocarbon substance dissolved in the solvent entering the terminalzone is precipitated and a continuous reflux is produced of theprecipitated substance whose properties are intermediate those oftheextract and those of the raflinate and which would overwise beincluded in the extract. In such case such conditions of the temperaturein all other parts of the system should be maintained as to cause thesolvent to possess a comparatively high solvent power.

Similar results may be accomplishedby, in-

not withdrawn as'a side stream irom a pipe through which the oil phaseis discharged from a selected point to the left of the point of feed ofthe incompletely refined material.

The construction illustrated in Fig. 2 com-.

prises a series of mixers Ml, M2, M3, M4, M5,

M8, of the character above described, each adapted to discharge itscontents through a suitable pipe into a correspondingseparator Al,

A2, A3, A4, A5, A6. The rawor incompletely refined substance is suppliedfrom a suitable source (not shown) through a pipe 2| to a pump 22 fromwhich it is forced through a pipe 23 into a header 24 having branches25, 26, 21, 28, 29, and 30, leading to the respective mixers Ml to M6,and provided with suitable valves to enable the raw or incompletelyrefined substance tobe delivered to another selected mixer.

The system will be described with the assumption thatthe raw orincompletely refined substance is delivered to one of the intermediatemixers, for example, M3. The solvent is supplied to the mixer MS from asuitable source (not shown) through a pipe 3|, pump 32, and pipe 33.

The rafflnate is discharged from the separator A8, through the pipe 34,while the spent solvent and extract is discharged from the separator Alat the opposite end of the system through the pipe 35. Suitable heatexchangers 36 and 31 are, provided to maintain a temperature gradientbetween the separators of the zones from which the solvent andextract-are expelled on the one hand and the rafiinate .is expelled uponthe other.

In the apparatus disclosed in Fig. 2, as in that disclosed in Fig. 1,pipes Ol, 02, 03. O4, O5, carry the material discharged from theseparators Al to A5 respectively to the mixers M2 to M8. respectively,while pipes SI, S2, S3, S4, S5,

deliver the solvent phase from the respective moved fr 0m any one of thepipes carrying the troducing into and mixing with the material in stagescomprising the separators Al and A2, es-

the terminal zone from which the spent solvent is expelled a materialmiscible with the solvent used and of such nature as will causeartificial miscible with the solvent to a pump 19 from which it isforced'through a pipe 20 into the mixerfl or, as shown, into the pipe itfrom which the solvent phase is discharged from the separator 4 into themixer I. -Such precipitation may be effected by the use of theprecipitant by'itself or in conjunction with'the maintenance of thetemperature gradient in the manner above described. In either of theconditions above stated the intensity of the'precipitative means andconsequent precipitation of artificial nature may be so regulated as toproduce products of predetermined quality and yield.

Fig, 2 illustrates a more highly developedap" paratus for performing theprocess forming the subject matter of the raw or incompletely refinedsubstance may be selectively introduced into any one of the severalmixers of the system and a desirable prodinvention' in which the oilphase.

Assuming that the raw or incompletely refined I substance is introducedinto the mixer M3, the operation indicated in Fig. 2 is, excepting forthe stage corresponding to separator A3, and the precipitated materialis returned to the rest of the system through the pipe OI. It will benoted that artificial precipitation is brought about exclusively in theseparator AI, thereby insuring the benefit of the entire system forextraction of the'precipitatod material. In some instances it ispossible that this precipitated material will be so lean in materialsworthy of inclusion in the raflinate that it may be desirable to remove,a portion of it and this can be accomplished by the removal of a sidestream from one of the pipes 38 or 39. This is analogous to the removalof the side stream of a rectifying column.

The raw material being introduced to mixer M3 where it is mixed with thesolvent phase issuing from separator A4. through pipe S3 and expelled toseparator A3 from which the undissolved portion will continue in asimilar manner consecutively to mixer M4, separator A4, mixer M5,separator A5, mixer M6, separator A6, from which it is expelled from thesystem as a finished raflinate containing small quantities of dissolvedsolvent.

The fresh solvent is introduced as heretofore described to mixer MS fromwhence it passes to separator A6, mixer M5, separator A5, mixer M4,separator A4, mixer M3, separator A3, mixer M2, separator A2, mixer Miand separator Al from which it. is expelled as spent solvent containingthe extract. In the course of such operation mixers Ml to M6 andseparators Al to A6 perform the functions heretofore described and maybe employed in any desirable number. the hydrocarbon substance is fedinto the system at a point other than that from which the spent solventis expelled, a portion of the extractive system is reserved forpreliminary partial refinement of the reflux before any portion of saidreflux is returned to the point of feed.-

In the performance of the process by the apparatus above described theportion of the apparatus to the left of feed may be considered analogousto a rectifying system, in that its operation results in increasedpurity of the extract, while that portion of the apparatus which is tothe right of the feed is analogous to a stripping section in that itsoperation results in a high removal of extract, or conversely a highpurity of rafiinate. It therefore follows that the process heretoforedescribed will result in a maximum yield and purity of both extract andraflinate.

By providing means for selectively supplying the raw or incompletelyrefined substance to any mixer of the series a delicate control may bemaintained in respect to the refinement of any particular material byproperly correlating the condition of the terminal zone, the point offeed of the incompletely refined substance, and the point of removal ofthe intermediate material with the qualities and yields of the products.

The material whose properties are intermediate those of the raflinateand those of the extract may be precipitated into and returned to thesystem in the apparatus disclosed in Fig. 2 by introducing a suitableprecipitant into the mixer Ml at the solvent terminal zone. It will benoted that the precipitating material is injected into the terminal zonefrom which the spent solvent is expelled from the system, therebyinsuring to the material precipitated therein the benefit of the entireextractive system. Any suitable means may be provided for injecting theprecipitant into the mixer Ml as, for example, a pump 43 in a pipe line44 leading from a suitable source of supply to the mixer Ml or pipe 25,the pipe 44 being provided with a valve 45 which will enable theselective use of the precipitant. The apparatus disclosed in Fig. 3comprises an upright vessel or tower 46, preferably of cylindrical form,having mounted therein a rotating Where changing fluid is circulated islocated in proximity to the top of the vessel. A discharge pipe 53 forthe spent solvent with the dissolved extract therein communicates withthe vessel preferably at its highest point, while a similar dischargepipe 54 for the rafllnate communicates with the vessel preferably at itslowest point.

Desirably one or more annular catch basins are provided intermediate ofthe length of. the tower. These catch basins may be of like constructionand comprise a horizontal base 55 fitting tightly within and secured tothe cylindrical wall or the vessel and an upwardly extending annularflange 56 located at a suitable distance from the wall of the vessel toprovide a catch basin 51.

In the operation of the device the heavier material will deposit in thebottom of the catch basin until it fills the catch basin and overflowsinto the descending stream. This heavier material may be drawn off inany suitable manner as by pipes 58 which may be discharged'into asuitable receptacle or may communicate with a header 59, suitable valvesbeing provided in the pipes 58 to enable the heavier material to bedrawn off from any selected catch basin.

The operation of the apparatus shown in Fig. 3 is as follows: It beingassumed that in the operation the solvent constitutes the lighter of thetwo primary materials entering the system; such being the case the,incompletely refined or raw material will enter the system through thepipe 49, from thence continuing downwardly through the vessel.Concurrently, "the solvent is introduced through the pipe 50 continuingupwardly through the' vessel, being maintained in intimate contact withthe incompletely refined or raw material by the action of the mixingdevice 41 and 48. After passing the pipe 49 through which the rawmaterial is introduced the solvent continues upwardly to the solventclarifying zone 60 at the top of the vessel at which zone artificialprecipitation of a material whose characteristics are intermediate ofthose of the extract and those of the rafilnate is effected in themanner heretofore described.

By. reason of the temperature gradient thus maintained in the vessel bymeans of the heat exchangers 5i and 52 a gradient of parafiinicity isestablished so that material of high paraffinicity will be concentratedat the lower portion or clarifying zone 6| of the vessel, and converselymaterial of high naphthenicity or low parafiinicity will be concentratedat the top of the vessel, whereby an extract of increased naphthenicityand a r'aifinate of increased paraflinlcity will be dischargedrespectively from the pipes 53 and 54. In such cases as there may exista considerable'portion of material intermediate in vertical shaft 41driven in any suitable manner (not shown) and provided with a series ofmixing arms or paddles 48 and having a feed pipe 49, preferablyintermediate of its length through which the raw or incompletely refinedsubstance is introduced into the vessel. The solvent is inv troducedthrough a pipe 50, preferably at a point characteristics of the desiredextract and the desired raflinate, such material may be withdrawn from acatch basin located at such selected height in the vessel as maydetermine the character of the intermediate material to be withdrawn.

Means may also be provided for alternatively introducing a precipitantinto the solvent terminal zone to precipitate material havingcharacteristics intermediate of those of the extract and those of theraflinate as in the apparatus previously described. This may beaccomplished by drawing the precipitant from a suitable source (notshown) through a pipei! by a pump 63 and injecting the-same through apipe 64 into the clarifying zone 60 at the upper end of the vessel.Where a precipitant is thus employed the temperature at both ends of thevessel may be maintained equal, or by the previously designatedapparatus the precipitant may be used con-Jointly with the propertemperature gradient, in either case correlating the amount ofprecipitated material to the quality and yield of the products.

By reason of the present invention therefore when employed in thetreatment of petroleum, or other base materials for the productlonoflubricating oil, a maximum yield of highly refined oil is recovered asthe rafllnate, while lubricating oils which are commercially useful butof less desirable quality may be recovered from the side stream.

While the process of solvent extraction is defined herein as applied tothe recovery of lubricating oil from an incompletely refined sub:-stance, such as a petroleum cut, it' is obviously ,applicable to thesolvent separation of other incompletely refined or raw materialscomprising components which vary in solubility with respect to thesolvents used. The disclosures therefore of the particular uses of theprocess herein described are of an illustrative character and are notrestrictive of the meaning and scope of the following claims.

What I claim is: I 1. In a process for refining hydrocarbon mixtures bythe action of a selective solvent in a continuous countercurrentoperation wherein a raifinate phase passes countercurrent to and in iiicontact with an extract phase, and in which an extract is dis-chargedfrom the countercurrent operation at a terminal stage, the improvementwhich comprises continuously mixing a precipitating'agent soluble in thesolventwith and dissolving it in the solvent in said terminal stagethereby to continuously produce a precipitate comprising a portion ofthe dissolved hydrocarbons having properties which are intermediatethose of the extract and rafilnate, passing the resulting precipitatedhydrocarbons from said terminal stage countercurrent to said extract"phase, and maintaining the conditions in all.

other parts of the countercurrent extraction operation such as willmaintain the solvent at an essentially constant solvent power ofpredetermined optimum efiiciency.

2. A process for refining hydrocarbon mixtures as defined in claim 1- inwhichsaid improvement further comprises the use of crotonaldehyde as theselective solvent in the countercurrent operation.

tures, which comprises subjecting the hydrocarbon to be refined to theaction of crotonaldehyde as a selective solvent in a continuouscountercurrent operation wherein. a raflinate phase passescountercurrent to and in contact with an extract phase, an extract beingdischarged from the countercurrent operation at a terminal stage,continuously mixing acetaldehyde as a precipitating agent soluble in thesolvent with and dissolving it in the solvent in said terminal stagethereby to continuously produce a precipitate comprising a portion ofthe dissolved hydrocar- 3. A process for refining hydrocarbon mixbonshaving properties which are intermediate those of the extract andrailinate, passing the resuiting precipitated hydrocarbons from saidterminal stage countercurrentto said extract phase in saidcountercurrent operation, and maintaining conditions in all otherpartsof the countercurrent extraction operation such as will maintainthe solvent at an essentially constant solvent power of predeterminedoptimum efliciency.

4., The process of refining a hydrocarbon substance by the selectivesolvent action of crotonaldehyde in a system in which continuouscountercurrent fiow of crotonaldehyde and said sub.-' stance is utilizedwhich comprises causing precipitation-of a portion of the hydrocarbonsubstance dissolved in the crotonaldehyde entering the terminal zonefrom which. the solvent phase is expelled from the system by introducinginto. mixing with and dissolving in said solventphase in said terminalzone, water, thereby to produce a reflux material which containssubstances desirably tobe included in the rafilnate but which wouldotherwise be included in the extract, and

maintaining such conditions in all parts of the extractive system "aswillcause the solvent to possess a comparatively high solvent power.

5. The process of refining a hydrocarbon substance by the selectivesolvent action of crotonaldehyde in a system in which' continuouscountercurrent flowtof crotonaldehyde and said substance is utilizedwhich compris'es causing precipitation of a portion of the hydrocarbonsubstance dissolved in the crotonaldehyde entering the terminal zonefrom which the solvent phase'is expelled from the system by introducinginto -mixing with and dissolving in said solvent phase in said terminalzone, acetaldehyde, thereby to produce a reflux material which containssubstances desirably to be included in the raffinate tract, andmaintaining such conditions in all parts of the extractive system aswill cause the solvent to possess a comparatively high solvent power.

6. A process for the separation of oil into parafilnic andnon-parafiinic fractions which comprises commingling said oil with aselective solvent and thereby forming a rafflnatephase contalningparaflinic oil fractions and an extract phase containing selectivesolvent and dissolved oilfractions, separating said phases, commin glingsaid extract phase with an anti-solvent, said anti-solvent being moresoluble in the extract phase than in the raffinate phase and adapted tocause separation of the extract phase into two layers, one layercontaining oil fractions relatively more parafllnic in character thanthe other of said layers, separating said layers, returning the moreparaffinic oil layer to the extraction system, and maintaining theconditions in all other parts of the extraction system such as willmaintain the solvent at an essentially constant solvent power ofpredetermined op .other of said layers, separating said layers,returning the more paraffinic oil layer to the extraction system at apoint between the points of introduction of oil to, and extract phaseremoval from, said system, and maintaining the-conditions. in all otherparts of the extraction system such as will maintain the solvent at anessena ing the terminal zone from which the solventphase is expelledfrom the system by introducing into mixing with and dissolving in saidsolvent phase in said terminal zone a precipitating substance misciblewith said solvent phase and by abruptly reducing the temperature of thesolvent as it enters the terminal zone, thereby to continuously producea reflux of precipitated substance the properties of which areintermediate those of the extract and the rafilnate and which wouldotherwise be included in the extract, and maintaining such conditions inall other parts of the systemas will cause the sqlyent to possess aconstant comparatively high soivn power.

9. A processfor the separation oi as defined by claim 6 in which saidselective s vent is crotonaldehyde.

10. The process of refining a hydrocarbon su stance as defined by claim8 in which said selective solvent is crotonaldehyde.

11. A process for the separation of oil into parafllnic and non-paramnicfractions, which comprises commingling said 011 with a selective solventfrom the group consisting of crotonaldehyde, acrolein, nitrobenzene andiurfural, and thereby forming a raifinate phase containing parafiinicoil fractions and an extract phase containing selective solvent anddissolved oil fractions, separating said phases, commingling saidextract phase with an anti-solvent from the group consisting of water,acetone and acetaldehyde, said .antisolvent being more soluble in theextract phase than in the rafilnate phase and adapted to causeseparation of the extract phase into two layers, one layer containingoil fractions relatively more parafllnic in character than the other ofsaid layers, separating said layers and returning the more paraflinicoil layer to the extraction system.

12. The process of refining a. hydrocarbon substance by the selectivesolvent action of a solvent selected from the group consisting ofcrotonaldehyde, acrolein, nitrobenzene and'iurfural in a system in whichcontinuous countercurrent flow of solvent and substance is utilized,which comprises causing precipitation of a portion of the hydrocarbonsubstance dissolved in the solvent entering the terminal zone from whichthe solvent phase is expelled from the system by abruptly reducing thetemperature of the solvent as it enters the terminal zone and byintroducing I into, mixing with, and dissolving in said solvent cludedin the extract, and maintaining such con-- ditions in all other parts ofthe system as will cause the solvent to possess a comparatively highsolvent power.

13. A process for the separation of oil containing paraflinic andnon-paramnic constituents into fractions containing such constituents,which comprises commingling said oil with a selective solvent andthereby forming a rafiinate phase containing parafllnic oil fractionsand an extract phase containing selective solvent and dissolved oilfractions, separating said phases, abruptly reducing the temperature ofthe separated exparaflinic in character thanthe other of said layers,separating said layers and returning the more paraflinic oil layer tothe extraction system.

JOHN WARD POOLE.

